I'm not sure about a rotary drum bioreactor, but if you're looking for low cost photobioreactors, there are a few options. However I'm skeptical of PBRs when it comes to large scale cultivation. But these PBRs have to be promoted because they might come handy in encouraging algae cultivation for domestic purposes in small scale. One such interesting video I'd like to share with you guys is - http://www.oilgae.com/videos/tags/Cheap-PBR